1. Field of the Invention
The subject matter of this invention relates generally to tapered fuse elements and relates in particular to tapered fuse elements having a length which is significantly larger than the width of depth thereof.
2. Description of the Prior Art
The use of current limiting fuses having areas of reduced cross sections is generally known. One popular way to provide areas of reduced cross sections is to notch a fuse link at the sides thereof. Examples of this may be found in the following U.S. Pat. Nos. 2,181,825, issued Nov. 28, 1939 to M. B. Wood, 2,816,989, issued Dec. 17, 1957 to E. W. Sugden, 3,386,062, issued May 28, 1968 to F. J. Kozacka, 3,394,333, issued July 23, 1968 to P. C. Jacobs, Jr., and 3,835,431, issued Sept. 10, 1974 to P. Rosen et al. Another common way to provide areas of reduced cross section is to provide central openings in the fuse ribbon. The openings are typically circular, rectangular, or triangular in shape. Examples of fuses with central openings follow: U.S. Pat. Nos. 3,319,029, issued May 9, 1967 to P. J. Jacobs, Jr.; U.S. Pat. No. 3,425,018, issued Jan. 28, 1969 to F. J. Kozacka, U.S. Pat. No. 3,471,818, issued Oct. 7, 1969 to R. E. Koch, and U.S. Pat. No. 3,523,265, issued Aug. 4, 1970 to J. Feenan et al. In addition to the preceding, fuses of reduced cross section are taught which have both central opening and notched edges. Examples of this type of fuse follow: U.S. Pat. No. 2,055,866, issued Sept. 29, 1936 to O. H. E. Jung et al and U.S. Pat. No. 3,465,275, issued Sept. 2, 1969 to K. W. Swain. Generally, all of the above-mentioned fuses have a uniform length and depth, but have reduced width at the areas of reduced cross section. Still another way to produce areas of reduced cross section is to provide a fuse with uniform length and width, but with scored or cut away portions of the fuse depth. An example of this kind of fuse element is as follows: U.S. Pat. No. 3,524,157, issued Aug. 11, 1970 To E. Salzer. Still another kind of fuse with areas of reduced cross section employs a notched side and a scored width. Examples of this type of fuse are as follows: U.S. Pat. No. 3,288.968, issued Nov. 29, 1966 to J. Feenan et al and U.S. Pat. No. 3,413,586, issued Nov. 26, 1968 to E. Salzer. Still another kind of fuse element with an area of reduced cross section comprises a fuse wire rather than a fuse ribbon, where the fuse wire has discrete discontinuities or a continuous tapers. Examples of this kind of fuse are shown in the prior art of FIGS. 5 and 7 of U.S. Pat. No. 3,848,445, issued Nov. 19, 1974 to F. L. Cameron and assigned to the assignee of the present invention. It is submitted that closest prior art to the present invention seems to lie in the kinds of fuse elements which have uniform depth, but tapered widths. Examples of these kinds of fuses are found in U.S. Pat. No. 3,743,994, issued July 3, 1973 to F. J. Kozacka (FIG. 2), British Pat. No. 445,902, dated Jan. 8, 1935 (FIG. 1) and British Pat. No. 514,916, dated May 18, 1938. In the latter patents, the length and depth of the fuse element are maintained generally constant, but the width thereof is varied. It would be convenient if a fuse element could be found which had all of the advantages of reduced cross section and a tapered longitudinal dimension, but which could nevertheless be drilled centrally or notched to provide other areas of reduced cross section for further improved current limiting action.